Parasitoid learning during interactions with ants: how to deal with an aggressive antagonist

Pauesia picta, P. pinicollis and P. silvestris (Hymenoptera: Aphidiidae) ar e common parasitoids of the conifer aphid Cinara pinea, which is regularly attended by red wood ants (Formica spp.). In this study, I tested whether f emales of these parasitoid species learned during interactions with honeyde w-collecting Formica polyctena workers that caution is not necessary if sea rching behaviour is adapted, and whether parasitoids benefit from being abl e to learn. When searching on Scots pines, naive females of P. picta and P pinicollis generally retreated to a pine needle when making contact with a honeydew-collecting ant, did not approach ants from the side or from the fr ont and kept a "safe distance" from ants when sitting on needles. After som e nonaggressive ant encounters, experienced female parasitoids changed thei r behaviour: they reduced their searching speed, approached ants from the s ide and even from the front, retreated less often in response to an approac hing ant and reduced the "safe distance". These experienced females had a s ignificantly higher rate of oviposition than naive females or females forag ing for an unattended host. Thus, the ability of the parasitoid to learn du ring interactions with an antagonist led to a prolonged retention time and a higher oviposition rate. By contrast, there was no evidence of learning i n P silvestris. Females of this species showed no behavioural change in res ponse to ant encounters, and there was no difference in the foraging succes s of naive and experienced female parasitoids.